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Measurement of Renal Function in Hemorrhagic Hypotension: Effect of Mannitol
TI-TE JOURNAL OF UROLOGY
Vol. 90, No. 2 August 1963 Copyright © 1863 by The Williams & Wilkins Co. Printed in U.S.A.
MEASUREMENT OF RENAL FUJ"\CTION IN HEMORRHAGIC HYPOTENSION: EFFECT OF lVIANNITOL GERALD P. MURPHY, JOHN A. GAGNON
AND
PAULE. TESCHAN
Frnm the Department of Suruical Physiology, Div1:sion of Basic Surgical Research, Walter Reed Ann.11 Institute of Research, Walter Reed Anny Medical Center, Washington, D. C.
The studies of Selkurt dern.onstrated that the the glomerular filtration rate (GFR) and effective renal plasma flow of the intact dog kidney remained relatively constant at blood pressures between 100 and 150 mm. Hg. 1 , 2 When blood pressure was reduced to 60 mm. Hg. or less, measurable urine flow and the clearances of para-aminohippuric acid (CPAH) and creatinine (CcR) decreased and varied widely. Data on inulin clearance (Crn) are not available from these studies. In addition, Selkurt 2 found the extraction ratios of P AH (
arterial cone. - renal venous cone.) art. cone.
utilizing the cannulated left renal vein and femoral artery in the dog to decrease progressively from values of +.90 reaching even negative values. Hence, in the presence of hypotension and low urine flow, directly measured renal blood flow (DRBF) showed reduced, continuing renal perfusion while clearance determinations approximated zero. .!Wore recently CPAH and Crn have been measured following hypertonic mannitol infusion in oliguric dogs and humans during or after episodes of hypotension due to hemorrhage or other causes.'' 4 The markedly elevated clearance values Accepted for publication February 1, 1963. 1 Selkurt, E. E., Hall, P. W. and Spencer, M. P.: Influence of graded arterial pressure decrement on renal clearance of creatinine, paraarninohippurate, and sodium. Amer. J. Physiol., 159: 369, 1949. 2 Selkurt, E. E., Hall, P. W. and Spencer, M. P. : Response of renal blood flow and clearance to graded partial obstruction of the renal vein. Amer. J. Physiol., 157: 40, 1949. 3 Barry, K. G., Doberneck, R. C. and McCormick, G. J.: The effect of hypertonic mannitol infusion on renal clearances of PAH (CPAH) and inulin (C,) in man: a comparison with water loading. Clin. Res., 10: 245, 1962. 4 Conte, N. F., Gagnon, J. A. and Barry, K. G.: The intrinsic renal effect of hypertonic mannitol infusion (HMI) on renal clearance of P AH (CPAH) exogenous creatinine (CcR), and urine flow (UF) during hemorrhagic shock in dogs. Clin. Res., 10:
246, 1962.
obtained shortly after the infusion of the mannitol during the resulting osmotic diuresis were thought to indicate a large and prompt increase in renal blood flow. Since the steady-state requirements for meaningful interpretation of clearance data were not met, further comparisons of DRBF with blood flow calculated froJTt clearance data were undertaken during controlled hemorrhagic hypotension with low urine flow and after hypertonic mannitol infusion. By using a specially devised bleed-out apparatus, 5 which constantly maintained a selected blood pressure (i.e. 50 mm" Hg. in this study) and gave continuous information on the volume of bleed-out, wide variation and unmonitored fluctuations in blood pressure and blood volume were avoidecl.6 MATJ,JRIALS AND METHODS
Twenty-five mongrel dogs of both sexes, weighing between 14 to 21 kg., were used. Anesthe~ia was maintained by 30 mg./kg. nembutal (Abbott). Jugular veins were cannulated for infusion of clearance substances and withdrawal of peripheral venous specimens. The left femoral artery was cannulated and connected for both to a mercury manometer or a pressure transducer monitoring of aortic blood pressure, and and to a bleed-out apparatus. 5 The right femoral artery was cannulated for easy access to peripheral arterial blood samples. The left kidney was exposed via a midline abdominal incision and loose ligatures were placed about the left renal artery and vein. The left ureter was exposed and cannulated with a small, double-lumen polyethylene catheter to the level of the renal pelvis. The inner lumen permitted saline and air washout. During occlusion of the renal artery for 5 Einheber, A. and Clarke, R. W.: Blood pressure stabilizing device and blood reservoir for inducing hemorrhagic hypotension. J. AppL Physiol., 11: 493, Hl57. 6 Finkle, A. L., Karg, S. J., Ballard, J.M. and Smith, D. R.: Effect of hemorrhage and fluid replacement on function of surgically reduced renal mass. J. Urol., 88: 464, 1962.
133
134
MURPHY, GAGNON AND TESCHAN
HEMORRHAGIC HYPOTENSION 50 mm Hg GFR
20 Ccr 10 (ml/min) 0 180
- - DRBF
160
...... RBF (!'.EAli x ..L.) EPAH
RENAL 140 BLOOD 120 FLOW 100 (ml/min.)
1-Hct
80 60 40 20 0 I ml/min.
14.... EPAH Ee,
.92 .32
.85 .28
81 .19
-.13 -.08
.60 -.19
.87 .25
.53 .17
.67 ]0 .18 20
.78 .24
.78 .17
.77 .I 9
URINE FLOW 0.5 (mi./min)
0 50
300
250
200
150
100
333
TIME- MINUTES
Fm. 1. Summary of typical results obtained from left kidney of dog with hemorrhagic hypotension, 50 nun. Hg. TABLE 1. Summary of data obtained chlring control, hemorrhagic hypotension, and hypotension at 50 mm. Hg plus 1nannitol inf,lsion (left kidney only) Expt. 22 Dog 4, UG, male 24.0 kg. Period Elapsed Time Urine Flow (min.) No. (cc/min.)
1 2
Control
0-20 21-42
.07 .06
CPAH
RBF
DRBF
CcR
CrN
50 49
116 117
154 158
16 17
16 15
Ern
.23 .26
EPAH
.70 .67
EcR
.13 .16
-------------------------------------------------
Hypotension + anuria
3
43-64
.02
14
114
25
4
4
4
65-108
0
0
0
28
0
0
.05 .05 .05 .06 .06
.20
- .13
- .16
-.06
-----------------------------------------------
Hypotension + mannitol 20% 2 cc/min.
RBF
5 6 7 8 9 10 11 12
109-140 141-149 150-156 157-162 163-173 174-195 196-228 229-244
0 .01 .05 .08 .05 .06 .05 .06
CPAH X _1_. EPAH 1-HCT DRBF = Direct Renal Blood Flow. =
9 13 23 22 15 13 6 6
46 57 112 81 63 50 16 29
35 38 39 40 43 48 53 60
0 1 1 1 1 0 0 0
1 2 3 2 1 1 1 0
.10 .08 .01 0 .03 -.01 .01 .02
.29 .33 .29 .38 .33 .36 .50 .27
.03 0 .02 .03 0 0 0 - .02
MEASUREMENT OF RENAL FUNCTION IN HEMORRHAGIC HYPOTENSION
+
45 '40
READINGS EVERY 10 MIN. TOTAL 13 DOGS
35 30
25 (CC/MIN.I
if
o
0
.,
& I!
Iii'
0
1l CHANGE DRBF (L) FOLLOW/NG o ~ e MANNITOL INFUSION r;,
c:;,
0
&
20
I5
13.5
in water was then given intravenously at rates of 1 to 5 cc/min. and observations continued for one or more hours. At the conclusion of each experiment (total duration 250 to 350 minutes) both kidneys were removed and weighed. The principles of laboratory animal care as promulgated by the National Society for Medical Research were observed. RESULTS AND DISCUSSION
0
~~'-:;;.-'-;;:-':~c:':-,..,.,.....,___'-'-.L...!-'-l-L...LW-J 10
SYSTEMIC BP IS 50 mm/Hq
30
50 70
90 I!O
130 150 170 190 200 230
MINUTES
Frn. 2. Measured increases in direct renal blood flow (left kidney) after mannitol infusion. about 45 seconds, the renal vein was cannulated with a polyvinyl catheter which led to an open reservoir. A side-arm access tube permitted withdrawal of blood samples for determination of extraction ratios (EPAH, EcR, Em). Blood was returned to the animal's left jugular vein from the reservoir by means of a sigmamotor pump via a Fisher heater at 38C. DRBF was then measured directly by reading from the pump calibration while the reservoir blood level remained constant. Heparin, 5 mg./kg., was given intra-arterially prior to cannulation. Respiration was maintained by means of a Harvard pump respirator and a cuffed endotracheal tube. Para-aminohippuric acid was determined by the method of Brun. 7 Creatinine and inulin were determined by the standard procedures previously reported from this laboratory. 8 Serial arterial and renal venous specimens were also obtained for determination of hematocrit and plasma total solids. 9 Following an hour of control observation of DRBF and sampling for CPAH, Cm, CcR and the extraction ratios, hemorrhagic hypotension was induced to a constant level of 50 mm. Hg. for 60 minutes. Observations were continued. Hypertonic (20 per cent) mannitol • 7 Brun, C.: A rapid method for the determination of para-aminohippurate acid in kidney functwn tests. J. Lab. Olin. Med., 37: 955, 1951. 8 Ladd, M., Lidd.le, _L. and Gagnon, J. A.: Renal clearance of mulm, creatinine, and ferrocyamde at normal and reduced clearance levels m 9the dog. Amer. J. Physiol. 184: 505, 1956. Barry, K. G., McLaurin, A. W. and Parnell B. L.: A practical, temperature-compensated hand refractorr_ieter (t.he TS meter): Its clinical use and application m estimation of total serum proteins. J. Lab. Olin. Med., 55: 803-808, 1960.
Figure 1 and table 1 summarize data obtained in a representative experiment in which is revealed the characteristic evolution of differences between renal blood flow (REF) calculated from CPAH, EPAH and the hematocrit) and DRBF. During sustained hypotension clearances are zero; however, DRBF continues at about of control rates. After mannitol infusion clearance of PAH is elevated as it is "washed" out" in the initial urine from the hypotensive and previously anuric kidney. A period of reequilibration follows with a fall in the factitious values of CPAH, CcR and Cm, until RBF again equals DRBF. The latter has risen slowly while the former rose and fell. Since such discrepancies were seen in all experiments, it is concluded that the great increase in renal blood flow as Sl\O'gested. by indirect clearance techniques followi;o-b manmtol infusion in hemorrhagic hypotensive states is chiefly a result of an artifactual "washout" by osmotic diuresis; it does not correspond ~o the small increase in DRBF actually measured, 1.e. 10 to 45 cc/min. after 100 min. of hypertonic mannitol infusion (fig. 2). The disparity between directly measured renal blood flow and that calculated from PAH clearance is summarized in figure 3. Analysis of urinary excretion of PAH as well as observed changes in its extraction ratio suggests the following sequence of events: During anuric hypotension DRBF is reduced. The renal tubules become saturated with PAH but are unable to maintain either the blood-to-lumen P AH gradient or the normal extraction and excretion process at reduced rates of perfusion and of luminal fluid flow. PAH then presumably diffuses back into the interstitium, elevates the venous concentration, and the extraction ratios become negative. Creatinine because of its smaller molecular size crosses tubular boundaries earlier and negative extraction ratios are recorded before those of P AH. Glomerular filtrntion apparently continues at a low rate in some
~s
136
MURPHY, GAGNON AND TESCHAN
2601 TOTAL 11 DOGS Sp= 50
180
mm Hq
170 150 130 CC/MIN JOO
70 50 30 10
oL_ _ __i__ _ _ _ ____:::::~E=-----------~L_ __J CONTROL
SHOCK
SHOCK+ MANNITOL
MANNITOL/ SHOCK CLEARANCES CLOSE
Fm. 3. Difference between RBF and DRBF after mannitol infusion in hemorrhagic hypotension, 50 mm. Hg. 1.0 . TOTAL II DOGS
ca a
.BO
00
A
0
C
C C i,C
00
A
C
C C
C
C
.40
cc
C
A
<9 ooO
"'
A
a C
C
C
a
C
C
a C
a
C
C
Ab{~.
C
C C
C
B
0
C
C C C 0 C O C A
"
0
A
AB
"' A
,5
1.5
1.0
2.0
2.5
3,0
CC/MIN./GM. KIDNEY
"'"'
"'
"'
.5
A
A
"' C
"'"' .3
0
A
.I
E)
0
A
'1_00o
A
EPAH
c
00
A A A
.20
8
C C
.60
(El
C C
C
A
A
C
"'
"' 0
CONTROL HYPOTENSION 50mtnHq HYPOTENSION 6 MANNITOL
.7 .9 I.I 1.30
Fm. 4. Summary of changing extraction values of P AH in relation to direct renal blood flow after mannitol.
MEASUREMENT OF RENAL FUNCTION IN HEMORRHAGIC HYPOTENSIOK
137
D BD
.8 D D
.7
~D
D
o§ D D
6 .5
©
.4
.3 .2 .I EPAH
0
.I .2 .3
.
o CONTROL
.4
.5
e
0
HYPOTENSION (50 mm Hq)
HYPOTENSfON
+
MANNITOL
.6
.7 .8 .9 1.0
.8 .7 .6 UPAH
.5
r
(mg¼) .4
.3 .2 .I
r
D
a
fu, :,,
a
f 1
0 2 PERIODS I CONTROL
D
g
3
.
\I
t
5 SHOCK
~
•
4
6
7
ANURIA
+
8
9 10 II SHOCK MANNITOL
12
13
+
SHOCK
Fm. 5. Summary of serial changes between
EPAH
and
nephrons during this hemorrhagic hypotension, accounting for the onset of diuresis without change in blood pressure. Because of its molecular size and configuration, mannitol remains within the tubular lumen and produces osmotic diuresis. Intratubular concentration of PAI-I, inulin, and creatinine are decreased permitting further extraction and excretion. The initial urine to reach the ureteral catheter is rich in PAR, and calculations of renal blood flow based on these elevated concentrations are necessarily erroneous. Figure 4 summarizes the shifts in extraction of PAR which occur following onset of mannitol diuresis. Loss of fluid having a high PAI-I concentration via the lymphatics is possible but not documented. PAR extraction is seen to shift from negative to positive and to rise toward control values after mannitol infusion is begun, even before measurable urine appears. Again, this suggests washout by mannitol of concentrated tubular fluid.
UPAH
after mannitol and hemorrhagic hypotension.
Figure 5 relates the urinary concentrations of P AH to the extractions during the principal phases of these experiments. The consistent increase in renal blood flow following hypertonic mannitol infusion remains to be explained. It was thought that a fall in hematocrit, plasma total solids, and protein could alter viscosity of the blood perfusing the kidney. Such measurements were made and 9, general fall was noted in each value. Blood viscosity was then calculated by the method of Lamport. 1° Figure 6 depicts the negati-rn result obtained: there was no relationship between the calculated change in viscosity and the increase in directly measured renal blood flow. Since it is possible that the formula is not applicable to this in vivo situation, no conclusion is derived" Nforeover, no correlation was found between 10 Lamport, H.: Improvements in calculation of renal resistance to blood flow. Charts for osmotic pressure and viscosity of blood. J. Clin, Invest., 22: 461, 1943.
I !
138
MURPHY, GAGNON AND TESCHAN
1.5 TOTAL 10 DOGS
0
1.0 0
.9
-1:,.µ.
.8
(VISCOSITY)
.7 .6
0
0 0
0
.5
Cb
s
.4
0
.3
0 0
0
.2 .I
0
os
0 0
0
0
+ 5
0
00
0
0
0
0
0
0 0 0
0
0 0
0
10
15
20
25
31
+6.DRBF (RENAL BLOOD FLOW)
FIG. 6. Graphic representation of failure of correlation between indirectly measured blood viscosity changes and increased DRBF after mannitol infusion. the increase in direct renal blood flow and change in bleed-out volume, i.e. the increase in DRBF was not apparently related to the tendency of the mannitol infusion to increase blood volume. According to the theory of Swann11 a change in the size of renal tubular lumens induced by osmotic diuresis could increase the interstitial vascular volume, decrease the vascular resistance, and thus indirectly produce an increase in renal blood flow. Alternatively, a direct effect on efferent glomerular arterioles is possible, as proposed by Lilienfield and associates,12 which may account for 11 Swann, H. G. and Ormsby, A. A.: Functional renal distention during diuresis. J. Urol., 82: 200, 1959. 12 Lilienfield, L. S., Rose, J. C. and Porfido, F. A.: Evidence for a red cell shunting mechanism in the kidney. Circ. Res., 5: 64, 1957.
increased renal blood flow, decreased GFR and decreased EPAH at least in normotensive states. The latter effects would be overshadowed in these experiments by the mechanisms previously discussed. SUMMARY AND CONCLUSION
Hypertonic mannitol may cause a small increase in directly measured renal blood flow during hemorrhagic hypotension. Wide discrepancies between renal blood flow values obtained directly and by clearance methods are documented during hypotension, before and during mannitol-induced osmotic diuresis. The results are interpreted in terms of sequential variations in rates of excretion of clearance substances and their extraction from the blood.
Vol. 90, No. 2 August 1963 Copyright © 1863 by The Williams & Wilkins Co. Printed in U.S.A.
MEASUREMENT OF RENAL FUJ"\CTION IN HEMORRHAGIC HYPOTENSION: EFFECT OF lVIANNITOL GERALD P. MURPHY, JOHN A. GAGNON
AND
PAULE. TESCHAN
Frnm the Department of Suruical Physiology, Div1:sion of Basic Surgical Research, Walter Reed Ann.11 Institute of Research, Walter Reed Anny Medical Center, Washington, D. C.
The studies of Selkurt dern.onstrated that the the glomerular filtration rate (GFR) and effective renal plasma flow of the intact dog kidney remained relatively constant at blood pressures between 100 and 150 mm. Hg. 1 , 2 When blood pressure was reduced to 60 mm. Hg. or less, measurable urine flow and the clearances of para-aminohippuric acid (CPAH) and creatinine (CcR) decreased and varied widely. Data on inulin clearance (Crn) are not available from these studies. In addition, Selkurt 2 found the extraction ratios of P AH (
arterial cone. - renal venous cone.) art. cone.
utilizing the cannulated left renal vein and femoral artery in the dog to decrease progressively from values of +.90 reaching even negative values. Hence, in the presence of hypotension and low urine flow, directly measured renal blood flow (DRBF) showed reduced, continuing renal perfusion while clearance determinations approximated zero. .!Wore recently CPAH and Crn have been measured following hypertonic mannitol infusion in oliguric dogs and humans during or after episodes of hypotension due to hemorrhage or other causes.'' 4 The markedly elevated clearance values Accepted for publication February 1, 1963. 1 Selkurt, E. E., Hall, P. W. and Spencer, M. P.: Influence of graded arterial pressure decrement on renal clearance of creatinine, paraarninohippurate, and sodium. Amer. J. Physiol., 159: 369, 1949. 2 Selkurt, E. E., Hall, P. W. and Spencer, M. P. : Response of renal blood flow and clearance to graded partial obstruction of the renal vein. Amer. J. Physiol., 157: 40, 1949. 3 Barry, K. G., Doberneck, R. C. and McCormick, G. J.: The effect of hypertonic mannitol infusion on renal clearances of PAH (CPAH) and inulin (C,) in man: a comparison with water loading. Clin. Res., 10: 245, 1962. 4 Conte, N. F., Gagnon, J. A. and Barry, K. G.: The intrinsic renal effect of hypertonic mannitol infusion (HMI) on renal clearance of P AH (CPAH) exogenous creatinine (CcR), and urine flow (UF) during hemorrhagic shock in dogs. Clin. Res., 10:
246, 1962.
obtained shortly after the infusion of the mannitol during the resulting osmotic diuresis were thought to indicate a large and prompt increase in renal blood flow. Since the steady-state requirements for meaningful interpretation of clearance data were not met, further comparisons of DRBF with blood flow calculated froJTt clearance data were undertaken during controlled hemorrhagic hypotension with low urine flow and after hypertonic mannitol infusion. By using a specially devised bleed-out apparatus, 5 which constantly maintained a selected blood pressure (i.e. 50 mm" Hg. in this study) and gave continuous information on the volume of bleed-out, wide variation and unmonitored fluctuations in blood pressure and blood volume were avoidecl.6 MATJ,JRIALS AND METHODS
Twenty-five mongrel dogs of both sexes, weighing between 14 to 21 kg., were used. Anesthe~ia was maintained by 30 mg./kg. nembutal (Abbott). Jugular veins were cannulated for infusion of clearance substances and withdrawal of peripheral venous specimens. The left femoral artery was cannulated and connected for both to a mercury manometer or a pressure transducer monitoring of aortic blood pressure, and and to a bleed-out apparatus. 5 The right femoral artery was cannulated for easy access to peripheral arterial blood samples. The left kidney was exposed via a midline abdominal incision and loose ligatures were placed about the left renal artery and vein. The left ureter was exposed and cannulated with a small, double-lumen polyethylene catheter to the level of the renal pelvis. The inner lumen permitted saline and air washout. During occlusion of the renal artery for 5 Einheber, A. and Clarke, R. W.: Blood pressure stabilizing device and blood reservoir for inducing hemorrhagic hypotension. J. AppL Physiol., 11: 493, Hl57. 6 Finkle, A. L., Karg, S. J., Ballard, J.M. and Smith, D. R.: Effect of hemorrhage and fluid replacement on function of surgically reduced renal mass. J. Urol., 88: 464, 1962.
133
134
MURPHY, GAGNON AND TESCHAN
HEMORRHAGIC HYPOTENSION 50 mm Hg GFR
20 Ccr 10 (ml/min) 0 180
- - DRBF
160
...... RBF (!'.EAli x ..L.) EPAH
RENAL 140 BLOOD 120 FLOW 100 (ml/min.)
1-Hct
80 60 40 20 0 I ml/min.
14.... EPAH Ee,
.92 .32
.85 .28
81 .19
-.13 -.08
.60 -.19
.87 .25
.53 .17
.67 ]0 .18 20
.78 .24
.78 .17
.77 .I 9
URINE FLOW 0.5 (mi./min)
0 50
300
250
200
150
100
333
TIME- MINUTES
Fm. 1. Summary of typical results obtained from left kidney of dog with hemorrhagic hypotension, 50 nun. Hg. TABLE 1. Summary of data obtained chlring control, hemorrhagic hypotension, and hypotension at 50 mm. Hg plus 1nannitol inf,lsion (left kidney only) Expt. 22 Dog 4, UG, male 24.0 kg. Period Elapsed Time Urine Flow (min.) No. (cc/min.)
1 2
Control
0-20 21-42
.07 .06
CPAH
RBF
DRBF
CcR
CrN
50 49
116 117
154 158
16 17
16 15
Ern
.23 .26
EPAH
.70 .67
EcR
.13 .16
-------------------------------------------------
Hypotension + anuria
3
43-64
.02
14
114
25
4
4
4
65-108
0
0
0
28
0
0
.05 .05 .05 .06 .06
.20
- .13
- .16
-.06
-----------------------------------------------
Hypotension + mannitol 20% 2 cc/min.
RBF
5 6 7 8 9 10 11 12
109-140 141-149 150-156 157-162 163-173 174-195 196-228 229-244
0 .01 .05 .08 .05 .06 .05 .06
CPAH X _1_. EPAH 1-HCT DRBF = Direct Renal Blood Flow. =
9 13 23 22 15 13 6 6
46 57 112 81 63 50 16 29
35 38 39 40 43 48 53 60
0 1 1 1 1 0 0 0
1 2 3 2 1 1 1 0
.10 .08 .01 0 .03 -.01 .01 .02
.29 .33 .29 .38 .33 .36 .50 .27
.03 0 .02 .03 0 0 0 - .02
MEASUREMENT OF RENAL FUNCTION IN HEMORRHAGIC HYPOTENSION
+
45 '40
READINGS EVERY 10 MIN. TOTAL 13 DOGS
35 30
25 (CC/MIN.I
if
o
0
.,
& I!
Iii'
0
1l CHANGE DRBF (L) FOLLOW/NG o ~ e MANNITOL INFUSION r;,
c:;,
0
&
20
I5
13.5
in water was then given intravenously at rates of 1 to 5 cc/min. and observations continued for one or more hours. At the conclusion of each experiment (total duration 250 to 350 minutes) both kidneys were removed and weighed. The principles of laboratory animal care as promulgated by the National Society for Medical Research were observed. RESULTS AND DISCUSSION
0
~~'-:;;.-'-;;:-':~c:':-,..,.,.....,___'-'-.L...!-'-l-L...LW-J 10
SYSTEMIC BP IS 50 mm/Hq
30
50 70
90 I!O
130 150 170 190 200 230
MINUTES
Frn. 2. Measured increases in direct renal blood flow (left kidney) after mannitol infusion. about 45 seconds, the renal vein was cannulated with a polyvinyl catheter which led to an open reservoir. A side-arm access tube permitted withdrawal of blood samples for determination of extraction ratios (EPAH, EcR, Em). Blood was returned to the animal's left jugular vein from the reservoir by means of a sigmamotor pump via a Fisher heater at 38C. DRBF was then measured directly by reading from the pump calibration while the reservoir blood level remained constant. Heparin, 5 mg./kg., was given intra-arterially prior to cannulation. Respiration was maintained by means of a Harvard pump respirator and a cuffed endotracheal tube. Para-aminohippuric acid was determined by the method of Brun. 7 Creatinine and inulin were determined by the standard procedures previously reported from this laboratory. 8 Serial arterial and renal venous specimens were also obtained for determination of hematocrit and plasma total solids. 9 Following an hour of control observation of DRBF and sampling for CPAH, Cm, CcR and the extraction ratios, hemorrhagic hypotension was induced to a constant level of 50 mm. Hg. for 60 minutes. Observations were continued. Hypertonic (20 per cent) mannitol • 7 Brun, C.: A rapid method for the determination of para-aminohippurate acid in kidney functwn tests. J. Lab. Olin. Med., 37: 955, 1951. 8 Ladd, M., Lidd.le, _L. and Gagnon, J. A.: Renal clearance of mulm, creatinine, and ferrocyamde at normal and reduced clearance levels m 9the dog. Amer. J. Physiol. 184: 505, 1956. Barry, K. G., McLaurin, A. W. and Parnell B. L.: A practical, temperature-compensated hand refractorr_ieter (t.he TS meter): Its clinical use and application m estimation of total serum proteins. J. Lab. Olin. Med., 55: 803-808, 1960.
Figure 1 and table 1 summarize data obtained in a representative experiment in which is revealed the characteristic evolution of differences between renal blood flow (REF) calculated from CPAH, EPAH and the hematocrit) and DRBF. During sustained hypotension clearances are zero; however, DRBF continues at about of control rates. After mannitol infusion clearance of PAH is elevated as it is "washed" out" in the initial urine from the hypotensive and previously anuric kidney. A period of reequilibration follows with a fall in the factitious values of CPAH, CcR and Cm, until RBF again equals DRBF. The latter has risen slowly while the former rose and fell. Since such discrepancies were seen in all experiments, it is concluded that the great increase in renal blood flow as Sl\O'gested. by indirect clearance techniques followi;o-b manmtol infusion in hemorrhagic hypotensive states is chiefly a result of an artifactual "washout" by osmotic diuresis; it does not correspond ~o the small increase in DRBF actually measured, 1.e. 10 to 45 cc/min. after 100 min. of hypertonic mannitol infusion (fig. 2). The disparity between directly measured renal blood flow and that calculated from PAH clearance is summarized in figure 3. Analysis of urinary excretion of PAH as well as observed changes in its extraction ratio suggests the following sequence of events: During anuric hypotension DRBF is reduced. The renal tubules become saturated with PAH but are unable to maintain either the blood-to-lumen P AH gradient or the normal extraction and excretion process at reduced rates of perfusion and of luminal fluid flow. PAH then presumably diffuses back into the interstitium, elevates the venous concentration, and the extraction ratios become negative. Creatinine because of its smaller molecular size crosses tubular boundaries earlier and negative extraction ratios are recorded before those of P AH. Glomerular filtrntion apparently continues at a low rate in some
~s
136
MURPHY, GAGNON AND TESCHAN
2601 TOTAL 11 DOGS Sp= 50
180
mm Hq
170 150 130 CC/MIN JOO
70 50 30 10
oL_ _ __i__ _ _ _ ____:::::~E=-----------~L_ __J CONTROL
SHOCK
SHOCK+ MANNITOL
MANNITOL/ SHOCK CLEARANCES CLOSE
Fm. 3. Difference between RBF and DRBF after mannitol infusion in hemorrhagic hypotension, 50 mm. Hg. 1.0 . TOTAL II DOGS
ca a
.BO
00
A
0
C
C C i,C
00
A
C
C C
C
C
.40
cc
C
A
<9 ooO
"'
A
a C
C
C
a
C
C
a C
a
C
C
Ab{~.
C
C C
C
B
0
C
C C C 0 C O C A
"
0
A
AB
"' A
,5
1.5
1.0
2.0
2.5
3,0
CC/MIN./GM. KIDNEY
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CONTROL HYPOTENSION 50mtnHq HYPOTENSION 6 MANNITOL
.7 .9 I.I 1.30
Fm. 4. Summary of changing extraction values of P AH in relation to direct renal blood flow after mannitol.
MEASUREMENT OF RENAL FUNCTION IN HEMORRHAGIC HYPOTENSIOK
137
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HYPOTENSION (50 mm Hq)
HYPOTENSfON
+
MANNITOL
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ANURIA
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8
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Fm. 5. Summary of serial changes between
EPAH
and
nephrons during this hemorrhagic hypotension, accounting for the onset of diuresis without change in blood pressure. Because of its molecular size and configuration, mannitol remains within the tubular lumen and produces osmotic diuresis. Intratubular concentration of PAI-I, inulin, and creatinine are decreased permitting further extraction and excretion. The initial urine to reach the ureteral catheter is rich in PAR, and calculations of renal blood flow based on these elevated concentrations are necessarily erroneous. Figure 4 summarizes the shifts in extraction of PAR which occur following onset of mannitol diuresis. Loss of fluid having a high PAI-I concentration via the lymphatics is possible but not documented. PAR extraction is seen to shift from negative to positive and to rise toward control values after mannitol infusion is begun, even before measurable urine appears. Again, this suggests washout by mannitol of concentrated tubular fluid.
UPAH
after mannitol and hemorrhagic hypotension.
Figure 5 relates the urinary concentrations of P AH to the extractions during the principal phases of these experiments. The consistent increase in renal blood flow following hypertonic mannitol infusion remains to be explained. It was thought that a fall in hematocrit, plasma total solids, and protein could alter viscosity of the blood perfusing the kidney. Such measurements were made and 9, general fall was noted in each value. Blood viscosity was then calculated by the method of Lamport. 1° Figure 6 depicts the negati-rn result obtained: there was no relationship between the calculated change in viscosity and the increase in directly measured renal blood flow. Since it is possible that the formula is not applicable to this in vivo situation, no conclusion is derived" Nforeover, no correlation was found between 10 Lamport, H.: Improvements in calculation of renal resistance to blood flow. Charts for osmotic pressure and viscosity of blood. J. Clin, Invest., 22: 461, 1943.
I !
138
MURPHY, GAGNON AND TESCHAN
1.5 TOTAL 10 DOGS
0
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.8
(VISCOSITY)
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10
15
20
25
31
+6.DRBF (RENAL BLOOD FLOW)
FIG. 6. Graphic representation of failure of correlation between indirectly measured blood viscosity changes and increased DRBF after mannitol infusion. the increase in direct renal blood flow and change in bleed-out volume, i.e. the increase in DRBF was not apparently related to the tendency of the mannitol infusion to increase blood volume. According to the theory of Swann11 a change in the size of renal tubular lumens induced by osmotic diuresis could increase the interstitial vascular volume, decrease the vascular resistance, and thus indirectly produce an increase in renal blood flow. Alternatively, a direct effect on efferent glomerular arterioles is possible, as proposed by Lilienfield and associates,12 which may account for 11 Swann, H. G. and Ormsby, A. A.: Functional renal distention during diuresis. J. Urol., 82: 200, 1959. 12 Lilienfield, L. S., Rose, J. C. and Porfido, F. A.: Evidence for a red cell shunting mechanism in the kidney. Circ. Res., 5: 64, 1957.
increased renal blood flow, decreased GFR and decreased EPAH at least in normotensive states. The latter effects would be overshadowed in these experiments by the mechanisms previously discussed. SUMMARY AND CONCLUSION
Hypertonic mannitol may cause a small increase in directly measured renal blood flow during hemorrhagic hypotension. Wide discrepancies between renal blood flow values obtained directly and by clearance methods are documented during hypotension, before and during mannitol-induced osmotic diuresis. The results are interpreted in terms of sequential variations in rates of excretion of clearance substances and their extraction from the blood.